Electronic system for measuring microwave transmission through a wave guide



ct. 1K9, 1948. L E, NORTON I 2,451,769

ELECTRONIC SYSTEM FOR MEASURING MICROWAVE TRANSMISSION THROUGH A WAVEGUIDE Filed June 11, 1945 4 Sheets-Sheet 1 I 'lj. 27 29 /FMIo Alva 6m GIMP/l5) BY C@ Q Oct. 19, 1948. E. NORTON 2,451,769

ELECTRONIC SYSTEM FOR MEASURING MICROWAVE TRANSMISSION THROUGH A WAVEGUIDE 4 Sheets-Sheet 2 Filed June 11. 1945 Oct. 19, 1948. l.. E. NORTON 2,451,769

ELECTRONIC SYSTEM FOR MEASURING MICROWAVE v TRANSMISSION THROUGH A WAVEG'UIDE Filed June 11, 1945 4'Sbeets-Sheet 3 1 l 1 1 1 1 l 1 l 1 1 l 11 nventor LOWELL E. NORTON Gttorucg @et 19, 1948. E, NORTN 2,451,769

ELECTRONIC SYS'fEM FOR MEASURING MICROWAVE TRANSMISSION THROUGH A WAVEGUIDE Filed June 11. 1945 4 Sheets-Sheet INVENTOR. LOWELL E. NORTN Arras/ffy ELECTRONIC S 2&599

YS'IEM FOR MESURING MICROWAVE TRANSMISSION TOUGH A WAVE'GUIDE Lowell' E. Norton, PrincetonJunction, N. J., as-

signor to Radio Corp oration of America, a corporation of Delaware A A .Application June 11, 1945, Serial No. 598,740

5 claims. l

generally to electronic This invention' relates detectors `and more particularly to Aan .improved devicev for detecting and .measuring extremely-- small mechanical displacements or` vibrations.

Brieily, the instantinvention comprises an improved electronic detector comprising a thermionic discharge tube having-means for generating a thin'sheet 'of electrons 'which is focused upon a'secondary-electron-emissive collector electrode, and in which 'a light movable shutter is inter- Dosed between the focused electronsource and` n 'I'he movable shutter is the electron collector. y mechanicallyA coupled to jan external device, of which themechanical displacementis to be detected, by means of a flexible diaphragm set into the evacuated envelope of the tube. Since the electron beam is focused to an extremely thin sheet, and since the shutter when at rest normally interrupts substantially all electron transmission to the collector electrode, very slight displacements ofthe shutter provide relatively high collector current and collector voltage variations.

One application of the invention is' in thel detection of mechanical vibratitmsl of small magnitude. Another applicati 'n measurements wherein the discharge `tube envelope is suspended and cushioned in a high inertia support in a manner whereby earthvibrations are transmitted substantiallyfonly to the movable; shutter. A third application of the invention is in the of microwave trans or coaxial transmission lines in combination with the devices'disclosed in applicants copending ap'- plication Serial No.. 598,739, illed -June 11, ,1945. In -sald copending application the microwave ii'elds propagated' along a waveguide or coaxialline provide mechanical displacemeht'of a thin'f conductive diaphragm formi ing means. The improve detecting tube disclos an extremely sensitiv energy propagated n upting the tube'electronbe'am as a function of tb e'vibration amplitude; n' A :lur-

on risvv in selsmographic detection and measurement, mission through waveguides nga portion .of theguidfv n ment comprising; the in-l stant invention includes 4the combinationof such, a wave responsive diaphragm -withthe vibration :lect is t'o provide an improved comprising a therinlonicy tube 4 oupled through a ilexible 1191.1 phragmsinrsaidenvelope to anexternal source of 2 therobject of the invention is to provide an lmproved method of and meansfor measuring microwave energy-propagated along a waveguide or coaxial transmission line by utilizing a ilexible conductive element'forming a portion of the wave guiding means and responsive to the microwave fields and an electron discharge tube having an electron shutter responsive to displacement of said diaphragm for generating an electric cur rent proportional to the magnitude of said microwave elds. An additional object of the invention is to provide a more efficient and sensitive means for detecting and measuring mechanical vibra-- tion. A still further object of the invention is to provide an improved vibration detector adaptable to seismographic measurements.

The invention will be described in greater detail by reference to the accompanying drawings of which Figure 1 is a schematic cross-sectional 9,@ elevational view showing the basic components of the vibration responsive thermionic tube, Figure 2 is a schematic cross-sectional plan view of said basic features of 'said tube, Figure 3 is an en- 1 v larged schematic diagram of the vibration-responsive .movable mechanical elements of said tube',l Figure 4 is a partially crosssectional, elevational View of a preferred embodiment of said tube, Figure 5 is a cross-sectional plan view of said preferred embodiment of said tube taken along the section line VV, F igure 6 is a cr0sssectionalplanview of said preferredembodiment of -said -tube taken .along the section line VI-VI, Figure .'l-is an vexploded perspective view. of the principal elements of said preferred embodiment of saidA tube, Figure 8'is a partially cross-sectional Vview-vofjafsecond embodiment of the'invention adapted, to measurementsv of microwavev energy propagated along a waveguide, and Figure 9 is a family of graphs illustrative ofthe operating char- 40 acteristicsof vthe invention. Similar reference charactersl are lapplied to similar elements vthroughout the drawings.y

`'Referring to Figures 1,'2` and 3, a thermionic heater element i supplied by currents derived A from an external'source (not shown) energizes an indirectly-heated cathode 3 which emits'electro'ns.. v The electrons -from'the cathode 3 are .l lforme'd into a constricted .beam by means of an ffapertur'ed j limiting electrode and thence are focused-into an :extremely thin at beam by means of'focusing electrodes 'l which, if desired,

may `beebiased by a source oi' potential `.(not

. shown). The focused -beaxn of electrons impinges upon a collector electrode 9 which, in con- Vlili junction with an electronmultiplier i5 of any ype, provides an output current Ib through held to the base plate 3,9 by means of an angle ttor I1 connected to a source of collector bracket 63 which is spot welded thereto.

I9. The secondary-electron-emissive collector 4l 'able shutter 2i comprising a ine wire and the shielding electrode 43e. comprise a single 1 is normally disposed in the path of the 5 vstage electron multiplier which increases the elecbeam intermediate the electron beam tron efficiency of the tube by a factor of about 4. meansA and the collector electrode, in- After preliminary adjustment of the position and relatively heavier portion which passes tension of the supporting spring 5I, the assembly a flexible diaphragm 21 forming a por- 'of the tube is completed and it is evacuated. Subhe envelope 29 of the thermionic tube. 10 sequent adjustment of the tube is obtained by ry portion of the shutter external of the varying the deflection voltage applied to the dem may be coupled to any external deection electrodes 9 and II for centering the iding a source of vibrations to be measfocused electron beam upon the ne wire portion he focused electron beam derived from 45 of the shutter when it is at rest. External sing electrodes 1 passes between beam y15v terminals in the base of the tube are provided for :electrodes 9 and I'I which maybe biased the heater I, the cathode 3, the beam deectng :ring the electron beam upon the thin electrodes 9 and I I, and the secondary-electron- `:ion 23 of the shutter 2|, whereby the emlssive collector 41'for applying suitable operatoeam is normally shielded from the c01- lng voltages thereto. If desired, other terminals ctrode I3. vIt should be understood that 20 may be provided for the limiting electrode 5 and Wire portion 23 of the shutter 2I should focusing electrodes 1. However, the limiting,

cross-section slightly larger than the focusing and apertured shield electrodes have Zion of the focused electron beamr at been found to operate satisfactorily when' grounde' of the shutter. ed to the base plate 39.

3 is an enlarged view of the movable 25 In Figure 8 the vibration detecting tube de- II vand the diaphragm 21 showing the 'scribed heretofore by reference to Figures 4, 5,

t of the ne wire portion 2 3 of the shut. 6 and 7 is shown coupled by means of the external h respect to the collecter electrode |3 ln shutter portion 55 and coupling link 3i to a. thin to displacement of an external dametallic diaphragm forming a portion of one :lement 30 which is coupled through e, 30 of the wide faces of a conventional rectangular l to the external end of the heavy shutwaveguide '55. The diaphragm 3l] comprises, for

`n 25 The perl-,lon of the flgure shown example, a circular screen ci the order of 1000 Iines indicates the relative displacement mesh and having a thickness of .2 mil. For some :ments in response to vibrations of the applications the diaphragm may be a solid thm diaphragm or element 3ll The me 35 film. The diaphragm 3U is stretched at one end ,e 33 Shown on the ne wire portion 23 of a pair of telescopic supporting rings 61 and 69 )Vahle shutter and colnoldlng with the which fit into a heavy bracket 1I which supports the Collector electrodo g3 indicates the both the waveguide 65 and the vibration detecting eetren beam which l's normally shleldod tube. The heavy bas'e portion 51 of the tube is collector electrode |3 40 tted into a conventional tube socket 13 which 4J 5, 6 and 7 Show the Construction of also is supported by the heavy bracket 1. For d embodiment ofthe vlbratlonqespom the sake of simplicity the socket connections or Vhereln the indirectly heated Cathodea' contacts are not shown. An aperture 15 in the ing electrode 5I beam f sl side of the telescopic rings lil and Gil and bracket lm doflectlng electrodggug Ileffrgg 1I permits the heavy external portion 53 of theby upper and lower brackets 35 and 31 tube shutter to be coupled to the linkage 3| fasheld to a. base 39 by means of a U tened to the center of the waveguide diaphragm rap 4I. A V-shaped Vertical shield 30 I3 having a rectangular aperture 45 is n.expl'lmed m apphcant s Cqpendmg apphca' tion identified heretofore, the microwave fields of Jacent to the end ofthe beam deecth t d 1 th .d 6

des 9 and II remote from the cathode 3. t e Wave propaga e a Ong e Wavegm e 5 provide mechanical displacement or deformation of the thin waveguide diaphragm Si! thereby proglssge glcteegogngesoocg viding vibrations responsive to the microwave deflected p V pulses or modulation. which are transmitted through the elements 3l, 53, 55 to displace the Si? cnlllglgsemregfag swlch ne wire shutter i9 with respect to the electron no the up er Sid s; fthabp Izlg beam normally focused thereon. The displacewhich rojct frs o tgnefo ie rale ment of the shutter permits the beam to reach 1d whh su ortm deuocug eee 60 the secondary-electron-emissive collector elecnlectrodes grille wr nnof tgn trode 41 and provides a collector current or volto e lr 49 is fastened to a heavier Wire por age which 1s a function of the microwave energy ich passes through, and is sealed to, a propagated along the Wavegulde' Since the vibration-detecting tube with `its lic diaphragm 55 which is sealed into 65 nter portion 5.' of the base 39 The built 1n electron multiplier 1s extremely sensi tive, the collector current It will probably be of .1*151011 49 0f the Shutter 1S Centered m sufficient magnitude to actuate directly the indi- Q 45 0f the Shield electrode 43 by Plecator I1 connected in series with the collector lustment of the support/lng Spring 5| voltage supply. However, since the tube imlamtained under constant tension by pedance is relatively high, for example 50,000 aid sprmg. The secondary-electronohms, the output voltage also will be sufficiently llector 41 and the shield electrode 43 high to actuate efficiently subsequent amplifiers relatively xed positions by means of a or voltage responsive indicating devices of known 9 and bottom plate 6I to which the types. tre crimped. The bottom plate 6I is 75 Figure 9 ls illustrative of the operating char- Lgular aperture 45 exposes a secondaryacteristics of the tube. The dash line graph Gm illustrates the -coll'ectorto-cathode transconductance as' a 'function of the beam deflecting voltage applied to thefd'eilecting elements 9 and il. 'llhe broken line curve Ib shows the corresponding variation in collector current. -It ,isseen that-avariation 'onetenth volt-'ln beam deflection potentialzprovides' fa.; change tif-L65 microamperes in collector current. .Since the beam deflection sensitivity of tubes of this type is of the order of`.004- inch per volt, 'e collector current change fof 65 microamperes is provided .by a corresponding'deiection of the electron beam off.000 4 inch.. AIt follows that if the electron beam is not deflected-but if the viinewire shutter 23 is? mechanically displaced a distance of .001 inch, a collector current change of 163 microamperes will result. Since the singlev stage electron multiplier disclosed herein provides a gain of the order of 4, the total current sensitivity will be of the order of 650 microamp'eres per .001 inch of displacement :of c

the fine wire shutter 23.

Since a tube ofthis type may be readilycon- -structed toopera'te with a' .collector impedance Zh of the order of 50,000 ohms, it follows that-the output voltage sensitivity of the device'will be of'l vthe order of 3 0'vo1ts per .001 inch deflection of enseres tive .diaphragm io 1.1.

. le penne er een 'anni said waveguide and movable in response to microwavel electrical stresses therein', an electro-mechanic'al device comprising electron beam generating means, beam collecting means and beam interrupting means, and means coupling said diaphragm to said electron beam interrupting means for moving said interrupting means relative to the patlrof said beam to control said beam as a function of said microwave transmission.

3.1A.' system for measuring microwave transmission througli a waveguide including an electro-mechanical device comprising en evacuated envelope, .said envelope j enclosing an electron source, asecondary electron-emissive anode, and a movable electron shutter element disposed between said-source and-said anode for selectively shielding said anode from electron irradiation, and means disposed externally of said envelope for moving-said element to selectively expose said anode to said electron irradiation whereby said .anojde -current .is a function of the displacement the fine wire shutterv23. The voltage sensitivityv l v. shutter displacement is indicated, by the -solid line graph Eb which indicates a collector voltage change of .3 volt 'for a shutter displacement of .00001 inch.

-Due .to the extremen' high Sensitivity of the device, it is desirable thatits frequency characteristicsas determined by .theshutter size, tension,andmass and by the natural period ofthe envelope diaphragm and the external linkage, b 1

such 'that its response is highly seleetivetoV the of said-externally disposed means, 'means for con'- necting said anode to an external device, a flex l ible .conductive section of the wall of said waveguide movable in response to microwave stresses therein, and means coupling said flexible waveguide section to said. externally disposed means whereby-said anode'cur'rent is a function of said microwave transmission.

4. A system ior measuring microwave transmission through a lwaveguide including an electro-mechanical device comprising an evacuated envelope, said envolope enclosing an electron source,. means for focusing electronsfro'm said source Ato form a fiat beam, an anode, a fixed vibration frequency to be detected inorderfthat otherspurious or fictitious frequencies vmay pro-l vide a minimum of noise signal output. The deapertured. shieldingv electrode disposed between said focusing means andsaid anode, said electrQde aperture' being inthe `.plane of said beam,` a .l

movable electron shutter element disposedbetween said focusing'means and vsaid apertured vice,however, isnotunusually sensitive to operating voltage variations-since it is.tl'ie'relativem'e-` chanical displacement of the electronbeam .and 7 the fine 'wire shutter whichprovidestheremarkable vibration` sensitivity.4

In the application ofl the-device. to .seis-inographicgrneasurements it wouldbe ,desirable-to" electrode inthe plane of saidbeam for selectively shielding said anode from.. electron irradiation, and'electron beamdeiiecting means disposed adjacent vsaid beam between saidsource and said .-shutterfelement for providing adjustment of the planeof said beam, means disposed externally of mount thvibration detecting tube in arcus'hion'ed l mounting havingrelatively Ahigh inertia. 1- lAlso the coupling bei'iweren` the .vibration and the earthshould responsive :shutter sirable high frequency vibrations which,v would provide ilctitiousindications.

' Thusjthe invention disclosedcomprises'a novel vibrationindicator and animproved method of and means.'for detectin`g.and indicating either external vibrations ormic'rowave energy propagated alongla guidedfwave transmissonsystem.

I claim .as my invention: 1. A system for measuring microwave transmission through a waveguide including a flexible.

conductives'ection of the wall of said waveguide movable in response to microwave stresses therein, an electro-mechanical device comprisingl electron beam generating means, vbeam .collecting means and beam interrupting means, and means coupling said flexible waveguide wallcsectionto said electronbeam interrupting means for moving said .interrupting means -relative to lthe path of said beam-to control said beam as said microwave transmission.

2. A system for measuring microwave transmission through a waveguide including a conducv be suciently .heavy and" should be s'ulciently damped to minimize undesaldfenvelope for moving said element to selectively expose saidanode to saidv electron irradia,-

tlonwhereby'said anode current is a function of the 1 displacement of said externally vdisposed means, meansfor connecting said anode to an external `device,fa flexible. conductive section of the wall ufo-said waveguide movable in response to microwave stresses therein, and means coupling said flexible waveguidev section to said extera function of nelly dlsposedxneans whereby said anode current is a yfunction ofsaid microwave transmission.

v5. .A'system ior measuring microwave transmission .through a waveguideincluding an electromechanical device comprising an evacuated envelope, said envelope enclosing an electron source, means for focusing electrons from said sourceto form a flat beam, an anode, a fixed apertured shielding electrode disposed betweenv said focusin'g means and said anode, said elecmovalble .electron shutter-'element disposed between said focusing meansand said apertured electrode in the plane of said beam for selectively shielding. sa'id .anode from electron irradiation, andv electron beam deecting means disposed adiacenti said' beam between 'said source and-.said shutterelement for-providing adjustment of the plane of said beam, and means including a ileztihle trede-'aperture being in the plane of said beam, a

arming a portion of said envelope 3ans disposed externally of said enving said element to selectively exiode to said electron irradiation anode current is a function of the of said externally disposed means, nnecting said anode to an external ibie conductive section of the Wall uide movable in response to microtherein, and means coupling said :uide section to said externally dis- .whereby said anode current is a yid 'microwave transmission.

LOWELL E. NORTON.

REFERENDIES @ETEN The following references are oi record in the iile of this patent:

Number 15 Number UNITED STATES PATENTS Name Date Hehlgans Dec. 18, 1934 Brett July 21, 1942 Clark Nov. 30, 1943 Jonkers Feb. 1, 1944 Gurewitsch Sept. 3, 1946 Labin Oct. 29, 1946 Y FOREIGN PAI'ENTS lCountry Date 

